Liquid Natural Gas Trucks (LNG)

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While the spotlight is on electric and fuel cell trucks these days, another green semi strategy is quietly gaining traction. Many fleets are pre-ordering Nikola and Tesla semis, but liquid natural gas trucks are already on the road. Companies like Cummins Westport build liquid natural gas (LNG) engines, not entire vehicles. So, unlike the companies with grand plans for changing the trucking industry, they don’t need to spend time on design, or building plants. Also, some LNG fueling stations already exist across the nation. That means some fleets can start using liquid natural gas trucks right away.

LNG is being touted as the preferred option over diesel while everyone waits for the trucks of the future. However, there are trade-offs to think about before switching over to the natural gas option.

Comparing Diesel and LNG Performance

Liquid natural gas trucks perform well in less challenging situations, but they’re not as powerful in general as traditional semis. For example, diesel engines can handle steep grades while hauling heavy loads. However, drivers of LNG trucks experience disappointment when putting their semis to that test.

Additionally, traditional fuel stops outnumber the LNG stations scattered across the nation. Not having refueling stations along all routes reduces their driving range. Plus, diesel gets more miles to the gallon. One gallon of diesel has more than 1.5 times the energy that one gallon of LNG.

The Safety Factor

Natural gas and diesel are both flammable, but LNG is more combustible. How much more? Diesel’s rating is moderately flammable while LNG’s rating is highly flammable. Plus, its vapor can ignite even at low temperatures, earning LNG the National Fire Protection Association’s highest hazard ranking. In contrast, diesel typically ignites only when heated. The safety factor means storing and transporting LNG requires more care.

Liquid Natural Gas Trucks and Diesel Engines and Emissons

Diesel engines have a reputation for polluting the air. They spew carbon monoxide into the atmosphere along with nitrogen oxide and other greenhouse gasses (GHG). Additionally, heavy duty trucks emit visible particles in the form of smog. Diesel particulates are actually a carcinogen, hence the recent introduction of DPFs to scrub diesel exhaust. The problem starts in the engine, because diesel doesn’t mix quite evenly in the ignition chamber. LNG, on the other hand, mixes better so it burns cleaner. The result, in theory, is fewer GHGs.

The results are theoretical because studies comparing the two types of engines have come up with different and inconclusive data. While LNG does mix more completely and burn cleaner, it can emit increased GHGs and ultra-fine particles. What’s more, liquid natural gas trucks emit methane. It’s a GHG that’s about 20 times stronger than carbon dioxide. However, diesel engines can cut specific GHGs like methane and carbon dioxide. Plus, fleets using green diesel with no sulfur may see a huge drop in emissions and pollutants overall. On top of that, new diesel technology goes even further to cut emissions. For example, recirculating exhaust gas reduces nitrogen oxide.

The Bottom Line: LNG Vs. Diesel Costs

When opting for liquid natural gas trucks over diesel, emissions aren’t the only trade-off. The cost is also six of one, half a dozen of the other. They’re both readily available, and production costs are similar. A gallon of diesel currently costs more than a gallon of liquid natural gas. However, LNG trucks’ low MPG means you’ll have to buy more of it to travel the same number of miles.

Then there’s the cost of replacing diesel trucks with liquid natural gas trucks. If you’re looking at buying new, you might be able to find a very basic diesel semi for as little as $80,000. Of course, start adding on features and options and the price tag quickly goes up. A diesel semi can easily cost around $100,000 and can even top $200,000. The cost of a basic LNG truck falls in the middle, at about $100,000. Alternatively, fleets can go the conversion route.  You’ll spend a fraction of the cost of a new truck on kits that transform diesel semis into liquid natural gas trucks.

It may be a while before electric and fuel cell trucks are available. In the meantime, technology developers behind diesel and liquid natural gas trucks continue the quest to make their products greener. No matter who succeeds, with cleaner air and a safer environment, we’ll all be winners.


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